New standards are making the delivery of internet-based and enhanced content through a television medium a reality. The Advanced Television Enhancement Forum (ATVEF) is a cross-industry group formed to specify a single public standard for delivering interactive and enhanced television experiences. The initial results of the ongoing collaborative effort are set forth in the ATVEF specification v1.1 r26, which is incorporated by reference. The ATVEF specification can also be found at http://www.atvef.com/library/spec1—1a.html. The ATVEF specification enables interactive television content to be authored using a variety of tools and deployed to a variety of television, set-top, and PC-based receivers. As the interactive television industry continues to develop more applications, the ATVEF standard will continue to expand.
The ATVEF specification furthers the convergence of personal computers and traditional television receivers. Predictions indicate that consumers will eventually own a single device that will have the widespread availability and ease-of-use of television, combined with the interactive power and flexibility of a PC. The ATVEF defines the standards used to create enhanced content for delivery over a variety of media, including analog (NTSC) and digital (ATSC) television broadcasts, and a variety of network formats, including wireless, cable, satellite, and the internet.
In addition to defining what enhanced television content looks like, the ATVEF specification also defines how the content is transported from the broadcaster to the receiver, and how the receiver is informed that it has enhancements available for a user to access. The display of enhanced TV content includes two primary steps: delivery of data resources (e.g. HTML pages) and display of named data resources that are synchronized by triggers. Triggers provide a link to the location of enhanced content. Two models of transport labeled “Transport type A” and “Transport type B” define the capability of networks to engage in one-way and/or two-way communication with a user.
Generally, the Transport type A model is for delivery of triggers by a forward path and for the pulling of data by a required return path. Transport type B is for delivery of both the triggers and the data by a forward path while the return path is optional. Specialized enhanced television receivers are generally required to display interactive television programming.
Transport type A is defined for ATVEF receivers that maintain a connection (commonly called a back-channel or return path) to the Internet. Generally, this network connection is provided by a dial-up modem, or can be provided by any type of bidirectional access channel (e.g. cable modem, DSL, TI, ISDN, satellite, etc.). Transport type A is a method for delivering triggers alone, without additional content. Because there is no content delivered with Transport type A, all additional data must be obtained over the back-channel, using the Uniform Resource Locators (URLs) passed with the trigger as a pointer to the additional content. For example, using the URL(s) in the trigger, content can be pulled from the Internet via one of the previously mentioned network connections.
Transport type B, on the other hand, provides for the simultaneous delivery of ATVEF triggers and the associated content. In this model, the broadcaster pushes the content to a user's receiver. The receiver then stores the content for later access. Transport type B uses announcements that are sent over the network to associate triggers with content streams. Generally, an announcement describes a content stream and may include information regarding bandwidth, storage requirements, and language (enhancements may be delivered in multiple languages). Since a Transport type B receiver stores any content that will be displayed, the receiver uses announcement information to make content storage decisions. For example, if a content stream requires more storage space than a particular receiver has available, the receiver can elect to discard some older content, or it may elect not to store the newer announced content stream. Receivers can be configured with varying amounts of local storage capabilities.
It should be noted that a single video program can contain both Transport type A data (e.g. broadcast data triggers) and Transport type B data (e.g. IP) simultaneously. This scenario is advantageous to target the widest range of receivers and therefore customers. Thus, both IP-based receivers as well as receivers that can only receive broadcast data triggers will be able to access the same information. Receivers can be configured to support only IP based trigger streams and ignore broadcast data triggers, to support broadcast data triggers in the absence of IP based triggers, or to support broadcast data triggers and IP based triggers simultaneously.
An ATVEF “binding” is the definition of how ATVEF runs on a particular network. The binding may support either or both Transport types A and B. Having one standard ATVEF binding for each network is necessary so that receivers and broadcast tools can be developed independently. The ATVEF binding provides the glue between the network specification and the ATVEF specification in cases where the network specification doesn't contain all the necessary information. Thus, for ATVEF to provide interoperability between broadcast networks and receivers, it is important that each physical network have only one binding. Additionally, it is equally important that each binding provide a fully comprehensive definition of the interface between the broadcast network specification and the ATVEF specification.
ATVEF has defined bindings for delivering data over IP (Internet protocol) multicasts as well as over NTSC (National Television System Committee) systems. Because the transmission of IP is already defined for virtually every type of television broadcast network, the binding to IP is considered a reference binding. With this reference binding, defining an ATVEF binding for a new network can be based upon a specification of how to run IP over that network.
To illustrate the binding mechanism, consider the binding of ATVEF to the NTSC video format. Here, the NTSC binding defines Transport type A using an NTSC-specific method, wherein ATVEF triggers are broadcast in line 21 of the vertical blanking interval (VBI). Transport type B, on the other hand, uses the IP reference binding for delivering IP datagrams over the other VBI lines.
Television enhancements for Transport type B include three related data sources: announcements (which can be delivered via the session announcement protocol (SAP)), content (which can be delivered via the unidirectional hypertext transfer protocol (UHTTP)), and triggers (which can be delivered via the trigger protocol over user datagram protocol (UDP)). Announcements are used to announce currently available programming to the receiver, can be broadcast on a single well-known multicast address and port, and have a time period for which they are valid. Announcements also indicate the multicast address and port number that the client can listen in on to receive the content and triggers. Details of the announcement and the announcement protocol are provided in section 3.1.1 of the ATVEF specification.
Triggers are real-time events broadcast inside IP multicast packets delivered on the address and port defined in the Session Description Protocol (SDP) announcement for the enhanced TV program. In general, when the client sees a new announcement on the known address and port, the client knows that there will be data available on the given content and trigger addresses. Triggers are also mechanisms used to alert receivers to incoming content enhancements. Among other information, every trigger contains a standard URL that specifies the location of the enhanced content. ATVEF content may be located locally (e.g., delivered over the broadcast network and cached to a disk) or it may reside on the Internet, another public network, or a private network (LAN/WAN). Triggers are described in greater detail in Section 1.1.5 of the ATVEF specification.
While broadcasters can utilize the features of an ATVEF based system to deliver enhanced information and programming to viewers, it is rarely practical to deliver the identical content to all end users. For example, advertising and other promotional material associated with a particular national television broadcast will not be uniformly applicable to all viewing markets and regions. It is thus desirable to modify or substitute certain information into the enhanced television broadcasts at various points in the broadcast distribution and to allow local and/or regional broadcasters to tailor a broadcast to their local market.